A group of students conducted an experiment to determine the growth of a certain type of plant over a 5-week period. The recorded heights of the plants (in centimeters) at the end of each week are as follows:

Week 1: 10 cm

Week 2: 15 cm

Week 3: 20 cm

Week 4: 25 cm

Week 5: 30 cm

To analyze the data, the students calculated the average growth per week. What is the average increase in height per week over the 5-week period?